Newly discovered organ may be lurking under your skin

Identified in mice, the simple organ most likely exists in humans, too, offering fresh insight into how we experience painful pressure and pricks.

A colorized microscope image shows the structure of a newly described organ called the nociceptive glio-neural complex, highlighted here in green. Nerve cells in this image are depicted in red, while cells in the outer part of the skin are shown in blue.

Most people who’ve been jabbed by a needle know the drill: First the pierce,
then the sharp, searing pain and an urge to pull away, or at least wince.
While the exact circuitry behind this nearly universal reaction is not
fully understood, scientists may have just found an important piece of
the puzzle: a previously unknown sensory organ inside the skin.

Dubbed the nociceptive glio-neural complex, this structure is not quite
like the typical picture of a complex organ like the heart or the spleen.
Instead, it’s a simple organ made up of a network of cells called glial
cells, which are already known to surround and support the body’s nerve
cells. In this case, the glial cells form a mesh-like structure between
the skin’s outer and inner layers, with filament-like protrusions that
extend into the skin’s outer layer. (Also find out about a type of simple organ recently found in humans, called the interstitium.)

An illustration of the glio-neural complex shows the location of this organ in the skin's inner tissue layer, or dermis (d), and the outer layer, or epidermis (d).

As the study team reports today in the journal Science, this humble
organ seems to play a key role in the perception of mechanical pain—discomfort
caused by pressure, pricking, and other impacts to the skin. Until now,
individual cells called nociceptive fibers were thought to be the main
starting points for this kind of pain.

“We have been thinking for probably a hundred years that pain is started
from nerves in the skin,” says study coauthor Patrik Ernfors,
a molecular neurobiologist at the Karolinska Institutet in Sweden. “But
what we show now is that pain can also be started in these glial cells.”

Pain progression

The team first identified this new organ in mice, and they tested its
functionality by measuring the rodents’ responses to different types of
pain. When the cells in the organ were turned off via gene editing, the
animals had a normal response to thermal pain, or discomfort caused by
heat or cold. But all of the mice showed a reduced response to mechanical
pain when the glial complex was deactivated.

The findings change the way scientists think about how pain begins and
progresses—at least in mice. The scientists have not yet checked that the
organ exists in humans, but Ernfors says the probability is high.

“Considering that all other previously known sensory organs in [mice]
also exist in humans, it is possible if not likely that this sensory organ
also is present in our skin,” he says.

“This is a very appealing discovery,” says Luana Colloca,
a neurophysiologist and an associate professor at the University of Maryland
School of Medicine who was not involved with the study. “It’s exciting
to know that there is a system that is much more than the nociceptive fibers
that we teach about to our students.”

PUBLISHED August 15, 2019

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